A variety of marking systems have been developed for marking a workpiece, such as with a Universal Product Code ("UPC") or the like. More particularly, a number of laser marking systems have been developed as shown by U.S. Pat. No. 5,309,273 which issued on May 3, 1994, U.S. Pat. No. 5,587,094 which issued on Dec. 24, 1996 and U.S. Pat. No. 5,605,641 which issued on Feb. 25, 1997.
A conventional laser marking system includes a laser source, such as CO.sub.2 laser or a yttrium aluminum garnet (YAG) laser oscillator, capable of producing a laser beam having relatively high power levels. Conventional laser marking systems also include a number of masks or templates which define the pattern to be marked upon the workpiece. The laser beam emitted by the laser source is generally deflected in a controlled manner in both the X and Y directions so as to be raster scanned across a mask. Typically, the deflection of the laser beam in the X direction is provided by a polygonal mirror which is rotated at a predetermined rate, while the deflection of the laser beam in the Y direction is provided by a galvanometer scanner or the like. After passing through the mask, the laser beam can again be deflected in the X and Y directions such as by a pair of galvanometers, so as to be directed to the surface of the workpiece which is to be marked.
The mask of a conventional marking system defines the predetermined pattern which is to be marked upon a surface of the workpiece. In order to imprint different patterns upon different workpieces, a laser marking system can include a number of different masks, each of which defines a different predetermined pattern. By inserting an appropriate mask into the path of the laser beam, conventional marking systems can mark a workpiece with the desired pattern. As such, the masks can be supported by a rotating wheel such that a different mask can be inserted between the laser source and the workpiece by controllably rotating the wheel. As will be apparent, laser marking systems that are designed to imprint a variety of patterns upon a workpiece generally require a large number of masks which must be repeatedly inserted into and removed from the path of the laser beam in order to mark a workpiece with the desired pattern.
Accordingly, liquid crystal masks have been developed. By applying appropriate voltages to the electrode lines defined upon the front and rear surfaces of a liquid crystal mask, a liquid crystal mask can be configured to permit light having a predetermined pattern to pass therethrough. By altering the manner in which voltage is applied to the electrode lines, however, the liquid crystal mask can be reconfigured so as to permit light having a different pattern to propagate therethrough. Thus, a single liquid crystal mask can define a number of different patterns by controllably applying voltages to the electrode lines on the front and rear surfaces of the liquid crystal mask. By utilizing a liquid crystal mask, the laser marking system no longer requires a plurality of different masks that must be repeatedly inserted into and removed from the path of the laser beam in order to mark a workpiece with different patterns. However, a liquid crystal mask is generally relatively expensive which correspondingly increases the cost of the laser marking system. Thus, while a variety of marking systems and, more particularly, a variety of laser marking systems have been developed, a need still exists for more economical laser marking systems.